Wood in the Landscape: Decks Part V
The distance between vertical railing members is determined by the diameter of a ball passing through the space. A 4- to 6-inch diameter is used by many codes. Some jurisdictions also require a height of 2 inches or less between the bottom rail and the decking surface.
The stair railings, treads, and risers are also controlled by code. Rail heights range from 30 to 38 inches measured from the front of riser. A 7- to 8-inch maximum rise and a 9- to 11-inch minimum tread is standard in most codes. The distance between vertical members on the stairs is the same as for a deck, and a 6-inch maximum from the bottom rail to the tread is usually required.
Before designing a railing, the local building codes should be consulted. It is common to extend the posts up through the decking as vertical supports for the top, bottom, and middle rails because the full length of the posts is used to resist the rail load.
When 4X4 posts are used to support the rails, the post spacing should not exceed 6 feet because the rails transfer the dead loads of the balustrades and rails to the posts. Greater spacing can cause the rails to sag. If the posts can't be extended through the decking, they can be bolted to the beams or joist framing; however this again places the stresses on the metal fastener.
A notched railing should be avoided because it has a tendency to split. All railing members should be particularly strong, and all connections firm and rigid, especially when the deck is at a high elevation. The railing provides a place for leaning and is often used to as a barrier to contain children.
A rail cap not only provides a horizontal surface to lean on or to place things on, but it also prevents water from penetrating the end grain of the posts. The rail cap should be angled to shed water away from the decking.
The cap also provides an opportunity to install fiberoptic strips or other forms of lighting. For special effect, lighting can be recessed into a routed channel on the underside of the cap or behind a horizontal member below the cap.
Daniel Winterbottom teaches in the University of Washington's Department of Landscape Architecture. His interests focus on urban and community landscape design, vernacular landscapes, therapeutic gardens, sustainable design, and the craft and detailing of built forms. He is principal of Winterbottom Design, a Seattle-based landscape architecture and site planning firm.
Wood in the Landscape: A Practical Guide to Specification and Design, copyright 2000 by Daniel Winterbottom, is available at bookstores and at Amazon. To order from the publisher, visit John Wiley & Sons or call 800-225-5945.
Note: photos in the book are in black and white.